Activated carbon and process of forming



Patented Sept. 6, 1932 UNITED STATES PATENT OFFICE PAUL ZURCHEB, OF FLORENCE, COLORADO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO CONTINENTAL OIL COMPANY, OF PONCA CITY, OKLAHOMA, A CORPORATION OF DELAWARE ACTIVATED CARBON AND PROCESS OF FORMING No Drawing.

The present invention relates to adsorbing or activated carbon and includes a method which will prepare or revivify such carbon, and impart to it such specially accentuated properties as special uses may require. It has particular reference to coke, such as petroleum coke, as a raw material.

Active carbon is now generally believed to be an amorphous carbon which is normally active, but which in preparation by ordinary methods of decomposing or carbonizing organic matter has its adsorbing qualities satiated with impurities that. are believed to be hydrocarbons present in the material. The aim of activation processes is the removal of such satiating substances, so that the normal activity may exert itself in desired directions. The same processes which activate are useful also to revivify, and in fact the initial activation may be considered as a revivification with special reference to the satiating substances which are formed simultaneously with the carbon. Consequently, in the following it is to be understood that activation and revivification may be used interchangeably, in spite of the fact that in technical practice there is a distinction, revivification being practiced at lower temperature than activation.

Various processes of activation are now in use, and are in general oxidation processes at high temperature. Agents and conditions are employed which selectively permit oxidation of the hydrocarbons present and prevent complete oxidation of the carbon.

Steam alone can accomplish this result and is desirable because all products are gaseous. Chemicals, such as sulphuric acid, or phosphoric acid, or zinc chloride, are used, but the carbon retains an appreciable percentage of residual chemicals which must be removed. Various other treatments have been proposed and practiced for removing these residuals, including washing, chemical treatments. heat treatments, etc. For phos phoric acid processes a subsequent heat treatmentwith steam has been employed to volatilize and sweep away the residual matter.

The activation processes require periods of time in the vicinity of ten hours, They Application filed August 13, 1928. Serial no. 299,441.

employ mostly vegetable matter as raw material, because coke does not give satisfactory products. Petroleum coke, obtained from pressure stills or from ordinary stills, may be activated with steam but gives a poor form for color adsorption. Its activity, if the raw material-is finely ground, is less than half of that of other activated carbons, and recovery in the activation process is only from 8% to 10% of the original coke. This is true of hydrocarbon-free' coke, as from the Burton process, and of coke relatively high in hydrocarbons, as from the Dubbs process.

Finely ground petroleum coke, activated with phosphoric acid as an oxidizer, yields a low grade product, having an activity not over about 25% of good carbons.

The primary object of this invention is the production of activated carbon.

One object of the invention is the provision of a new process of activating carbon and one which is effective on material, such as petroleum coke, that is not readily activated by other processes.

A particular object is to shorten the time of activation.

More specifically it is an object to use a type of material such as phosphoric acid, in such a way that subsequent removal of residual matter is not necessary.

It is a particular object to introduce'into a furnace containing carbon which has been activated in the presence of material such as phosphoric acid, a gas capable of sweeping out products which would otherwise be adsorbed and would appear as residuals subsequently to be removed.

It is still another object to use a chemically active cleansing gas which becomes advantageously effective in the process to activate, to regenerate other activating material, and to aid in removing residuals.

More specifically it is an object of the invention to provide a continuous activation process in which carbon and phosphoric acid move through a heated zone against a current of steam.

' The present invention is based upon the observation that when phosphoric acid and steam are used simultaneously, a better procmay be controlled by regulation of variable factors in the process.

With the foregoing objects and advantages in mind and with others that will be apparent, there is given herewith a more detailed explanation of the invention and a number of illustrative examples showing methods of carrying the invention into practice.

In the accepted phosphoric acid process the hydrocarbon content is removed by oxidation effects of the phosphorus oxides pres ent. Phosphorus, hydrogenated phosphorus, and lower oxides of phosphorus are discharged from the process. These are oxidized by suitable secondary recovery processes and reused. The carbon retains"soine of the products of reduction of phosphoric acid 0n cooling and these are subsequently washed out. Various otherch-"emical agents employed in other processes similarly produce residual products which are volatile at the activation temperatures.

By introducing steam into the activating chamber I have discovered that it has a mechanical cleansing action distinct f1;om its chemical action. It serves as a diluent for gases in the treating chamber and thereby prevents retention of volatile material, at the,

same time permitting escape of material already adsorbed. VViththis view of the invention it is contemplated that any of the well known processes employing chemicals such as phosphoric or sulphuric compounds, yielding products volatile at the activation temperature, may be immediately followed by a cleansing treatment with a gas. An inert gas like nitrogen, may be employed, although I use a chemically active gas like steam for other reasons.

I have found that the steam oxidizes the reduced phosphorus compounds and regencrates in the activation chamber the phosphorus compounds of higher oxygen content, such as the phosphoric acid and acids of lesser oxygen'content, so that they are still efi'ective as activating agents. The phosphorus compounds discharged from the furnace are therefore richer in phosphoric acid than when steam is not employed. Not only is the discharge richer in oxidizing agents but the gaseous atmosphere of the furnace has a higher proportion of oxidizing and activating compounds and a minimum of inactive residual phosphorus products. The steam acts as a catalytic agent, or as a vehicle for oxygen which is transferred to the phosphorus and other products of the reduction of phosphoric acid for activation purposes.

The internal reoxidation of the phosphorus compounds permits a unit quantity of it to be more effective, and contributes to the increased speed of the process. And the increased speed of the process, and the utilization ofthe steam no doubt minimizes the action of steam in burning up the carbon.

The Drocess may be operated as a batch process in several Ways. The regular chemical treatment, as with phosphoric acid, may be practiced until activation is partially or wholly completed. Then the cleansing treatment may be employed at or sufiiciently near the reaction temperature to secure the desired advantages. IVhen phosphoric acid and "steam as a cleansing agent are used a combination treatment is effected. If the activation is but partially completed, the steam and phosphoric acid will act together according to the combination of this invention. The reduced phosphorus products will be reoxidized and again made effective by the presence of the steam. Continuation of steam treatment to remove gaseous products from the furnace will free the activated carbon of any phosphorus compounds retained. These steps will eliminate washing of the product and subsequent regeneration of phosphoric acid. If the phosphoric acid process is carried on until the activation is complete,

the final steam treatment may be made with,

some of the advantages, except, of course, that the steam and phosphorus compounds cannot activate in combination, making the process longer, and different chemically.

I prefer to operate a continuous process to secure full benefit of all the important features of the invention. I use a continuously moving charge of carbon in a heated zone.

In the preferred practice of the invention I aim to move carbon and oxidizing agent against a stream of the cleansing gas. The

activation takes place as the material approaches the hottest zone of the furnace. The

cleansing gas is introduced near the discharge end and moves towards the hottest zone. It cools and cleanses the activated carbon and itself becomes heated. The hot gas pushes volatile products away from the discharge end, and away from the heated activated material. This prevents adsorption of such products and favors elimination of what may already be adsorbed.

The advantage of steam as a. cleansing agent is enhanced when phosphoric acid and its products of reduction are used as the oxidizer in the process. With the same arrangement as above described, carbon, suitably mixed with the phosphoric acid, is passed through the furnace against a current of water vapor introduced as steam at the discharge end. The mechanical action of the steam takes place as described and in addition there is chemical regeneration of the degraded phosphoric acid initially employed.

Carbon free of residue may be discharged, and the efiiuent gases arerich in phosphoric products that need not be regenerated. In the course of this reaction it is apparent that the carbon is first subjected to the action of phos phoric acid, then to the action of this material in combination with steam or its resultant products, and finally to the action of steam alone.

There is .a general belief that carbon which is deposited at lower temperatures tends to be active, while carbon deposited at higher tempe-ratures tends to be inactive. Some authorities have set the divldln'g limit 111 the vicinity of 600 C. For this reason it has been general practice in making activated carbon carefully to eliminate the volatile hydrocarbons by slow distillation at low temperature. It is possible that deposition of the inactive graphitic type of carbon at higher temperatures protects adsorbed hydrocarbons so that they are not readily oxidized in activation processes. lVhet-her these explanations are true or false, they are supported by the fact that coke does not yield good carbon on activation by prior processes. Such carbon has an activity of about 50% to 60% of the activity that can be produced when my improved combination process is employed; and the fact that coke yields sucha good carbon by my process indicates the above beliefs may not be well founded.

Example 1.In carrying out my process I employ a rotary furnace with a great many longitudinal fins or partitions to expose a large surface of the carbon. A rotational speed and pitch is chosen so that a particle may be retained in the furnace for a period of about three hours. This, however, is no limitation and it is to be understood that the time may be shortened or lengthened as desired.

At one end of the furnace I feed a mixture of petroleum coke and phosphoric acid, either as the anhydride, or in the form of orthophosphoric acid or meta-phosphoric acid of syrupy consistency. Coke containing 12% volatile matter ground to pass a 200 mesh screen has been employed in admixture with 20% of its weight of phosphoric anhydride in the syrupy form. This mixture is almost a dry powder. The heat of the furnace in- :reases to a maximum at a point removed from the discharge end. A furnace 12 feet long may have the point of maximum temperature three feet from the discharge end. Suitable feeding means introduces the material into the furnace at a controlled rate. The maximum temperature zone may vary over a wide range, for example, from 850 to 1100 C. If the temperature is kept at least as high as 900 C. to 950 C., all the phosphorous products can be removed from'the carbon. Steam, amounting to twice the weight of coke-acid mixture is introduced at the discharge end under low pressure, such as about 8 inches Water pressure. The time of passage is three hours. Re-

gasoline having 125% of sulphur as mercaptans, when the gasoline vapors are passed through the sand-carbon mixture at 350 C. to 500 C. E mample 2.If the process of Example 1 is operated so that the time of passage is 4 to 4 hours, the recovery is 35% of the initial coke. The same decolorizing test will show an increased decolorizing power of 900 c. c. to 1000 c. e. as compared to the 400 c. c. of the three hour run. Under the same conditions for refining gasoline, its power is nil. Merely varying the time factor has materially changed the special properties of the product. a By a large number of experiments I have ascertained that addition of phosphoric acidup to 50% of the coke employed will activate carbon by my combined process so that it is four times as active as when activation is produced by phosphoric acid without steam. It appears that volatiles should not be driven out of the raw material before mixingthe chemicals, or an inferior product results.

The process is therefore one which prepares active carbon from material having the characteristics of petroleum coke. The process can be modified so as to vary the particular properties desired, and carbons for special uses may be prepared. A saving of time is effected whatever the character of the raw carbon, and two steps or treatments may be combined into one process, so that one heating performs the functions of two heatings of the prior art. I

As an example of the modifications which may be made in my process I illustrate the formation of a granulated hard activated carbon. It is sometimes desirable to have a granulated form of carbon which is not soft, which will withstand shocks, pressure and friction, such as the carbon made from fruit pits and coconut shells.

I have discovered that my process can be used to treat ordinarily soft powdered petroleum coke so that it will yield such a hard granulated product.

Example 3. 100 parts of petroleum coke containing 12% volatile matter is mixed with a small percentage, say 15%, of liquid hydrocarbon, such as a residual oil, and 20% of phosphoric acid in an efiicient mixer. The resulting mixture is granulated in a suitable granulating device. Thegranulated raw material is then activated by a three-hour passage in my furnace using the combination steam and phosphoric acid treatment above given, employing steam equal to about the weight of the charge.

The above process gives a yield of 55% of the coke charged. Activity of the product may be expressed by its power to decolorize 900 c. c. of the methyl orange solution as given under Example 1.

Its power is also measured by an absorption of 12% of gasoline vapors at the temperature of melting ice. The product is therefore a good decolorizing carbon and a good refin ing agent for hydrocarbons in the vapor phase.

The above example illustrates the preparation of raw material for the activation process, and the method of activating raw material containing hydrocarbons in substantial quantities which are greatly in excess of the sa'tiating hydrocarbons which activation aims to remove.

The carbon prepared according to this invention is also capable of use like other activated carbons for absorbing and purifying processes, suchas the absorption of gases and vapors of the saturated type of hydrocarbon, as in the methane series, which are constituents of natural gases; for unsaturated and other gases, such as those arising in refining operations, particularly those from pressure stills; for absorption of casing head gas; for toxic gases, like those encountered in industry and in warfare, for purification of gases like carbonic acid by a selective retention of impurities from the gas when the absorbed gas is removed from the carbon.

In my copending application Ser. No. 299,442 filed August 13, 1928, I have described the phosphoric acid process and a related process employing sulphur with erence to the production of a hard-granulated carbon. In the present application I have claimed the two processes generically, and the phosphoric acid process specifically with general reference to carbon and specific reference to raw material such as petroleum.

coke containing or admixed with a hydrocarbon. In said copending application, I have cliamed the sulphur process specifically with general reference to carbon and specific reference to petroleum coke with contained or added hydrocarbon for the production of hard carbon.

Various other modifications will readily suggest themselves to those skilled in the art. The various examples herein given are not to be construed as limitations since the invention contemplates all such changes, alternatives, steps, combinations, and compositions as are comprehended within the scope of the appended claims defining the invention.

What I claim is:

1. The method of activating carbon which special refcomprises subjecting heated carbon to the action of a phosphorus compound as an activating chemical capable of forming volatile reaction products, and subjecting the resulting carbon to the action of steam at a temperature between 850 C. to 1100 C.

r 2. The method of activating carbon which comprises subjecting a moving mass of heated carbon to the action of an activating chemical capable of forming volatile reduction prod-- ucts, and subjecting the same carbon to a temperature between 850 C. to 1100 C. to insure removal of the volatile residual pllOS-' phorus compounds.

5. The method of activating carbon which comprises subjecting heated carbon first to the action of a phosphorus oxide .then to the combined action of the resultant material and steam, and then to the action of steam at a temperature between 850 C. to 1100 C to insure products.

6. The method of activating carbon which comprises subjecting a heated mixture of carbon and a phosphorus oxide to the activating reaction of the mixture with steam at a temperature between 850 C. to 1100 C.

7. The method of activating carbon which comprises subjecting heated carbon to the activating action of the reaction products of carbon, steam and phosphorus at a temperature between 850v to 1100 C.

8. The method of activating carbon which comprises subjecting heated carbon to the activating action of the reaction products of carbon, steam and phosphorus, and subjecting the product to the cleansing action of steam at a temperature between 850 C. to 1100 C. to insure removal of residual volatile products.

9. The method of activating carbon which comprises subjecting a moving mass of heated carbon containing phosphoric acid to the activating action of the mixture, introducing steam in counter-current to the moving mass, and subjecting theactivated carbon to the cleansing action of the steam at a temperature between 850 C. to 1100 C. I

10. The method of activating carbon which comprises moving a mixture of carbon and phosphoric acid through a heated zone against a current of steam at a temperature between 850 C. to 1100 O. to activate the removal of residual volatile carbon at the carbon feeding end of the heated zone, and to cleanse the activated carbon of phosphorus compounds by the action of steam at the carbon discharge end of the heated zone.

11. The method of activating carbon which comprises subjecting heated petroleum coke containing volatile matter to the combined activating action of phosphorus products and steam, at a temperature between 850 C. to

12. The method of activating carbon which comprises subjecting a heated mixture of. petroleum coke and a heavy hydrocarbon to the combined activating action of phos phorus products and steam at a temperature between 850 C. to 1100 .C.

13. The method ofactivating carbon which comprises subjecting a heated mixture of petroleum coke containing volatile matter and phosphoric acid to the combined activating action of the mixture with steam, and cleansing the carbon product with steam at a temperature between 850. C. to 1100 C.

14. The method of activating carbon which 1 comprises subjecting a heated mixture of one hundred parts of petroleum coke containing volatile matter, twenty parts of phos phoric acid and fifteen parts of hydrocarbon to the combined activating action of the mixture with substantially forty-five parts of steam at a temperature between 850 C. to 1100 C.

' 15. The method of activating carbon which comprises subjecting for substantially three hours a continuously moving heated granulated mixture substantially in the proportion of one hundred parts of petroleum coke containing volatile matter, fifteen parts hydrocarbon and twenty parts phosphoric acid, to the activating action of the mixture with substantially one third as much steam, and introducing the steam to the mass as a cleansing agent for the activated carbon at a temperature between 850 C. to 1100 C.

PAUL ZURCHER. 

